Cutter for forming twist drills



Patented Feb. 5, 1935 .UNITED 'STATES Bj-ATEINT `OFFICE CUTTER FOR FORMING TWIST DRILLS Harry A. Covill, Royal Oak, Mich., assignor to National Twist Drill and Tool Company, Detroit, Mich., a corporation of Michigan Application March 7, 1932, Serial No. 597,397

2 Claims. (Cl. 29--103) The invention relates t-o the manufacture of grooved blank and in projection therewith a diatwist drills and it is the object of the invention to grammatic plan of the cutter and the blank. The simplify and expedite the operations. In the cutter E has a portion F fashioned to form the present state of the art it is usual to perform groove A and continuous with this portion F a three distinct operations in fashioning the drill. second portion G which, in the position shown, is 5 The rst operation is the cutting of the spiral out of contact with the blank. However, if the groove or flute therein. A second operation is the blank is advanced along the axis 1-1 which is cutting away of the rear portion of the peripheral oblique to the plane 2-2 of the cutter and is siface intermediate the ilutes to provide clearance. multaneously revolved, the porti-on G will be lo The third operation is the removing of the burr brought into operative relation to the segment B l0 formed by the uting operation on the rear face and will cut the clearance D. Thus a cross secof the portion intermediate the flutes. These tion on the line 3-3 shows the portion F of the three operations are performed either in distinct cutter in engagement with the groove which is machines or in some cases such as turret maformed thereby While a cross section on the line chines, they are performed by distinct tools act- 4-4 shows a portion G in operative relation to l5 ing successively on the same blank. The reason the blank to form the clearance D while the porfor this Will be apparent when it is considered tion F is out of contact with the blank. that the drill blank is a cylinder and the milling Based on the principle just described, I have cutters employed have their teeth traveling devised a construction of cutter which may be in through a circular orbit. Itis therefore geometrithe form of an ordinary milling cutter gashed to cally difficult -or impossible to fashion a single form successive teeth, each of which has aportion tooth so that in rotating about the axis of the F and a portion G with an intermediate groove cutter it will simultaneously perform these several H and an oblique portion I at the left side of the functions on the different portions of the cylinportion F. Such a cutter when properly set in drical blank. I have, however, solved the probrelation to a rotating and axially advancing blank 25 lem through the design of a cutter which while will simultaneously cut the groove A and the having a series of like fashioned teeth operates clearance D with successive teeth thereof operwith dilferent portions of the same successively. ating on longitudinally spaced portions of the The invention therefore consists in the method blank. Therefore with a single operation both and construction as hereinafter set forth. of these two portions of the blank are properly 30 In the drawing: fashioned. Figure 1 is a side elevation of the cutter; As illustrated in Figures l, 2 and 5, J is the Figure 2 is a cross section thereof; rotary milling cutter having a series of teeth K K Figure 3 is a cross section through a drill showformed by transverse gashes L. Each of the teeth ing in dotted lines the blank from which it is is fashioned with a portion F for forming the 35 formed; groove or flute, a portion G for cutting the clear- Figure 4 is a diagram illustrating the principle ance in the peripheral portion intermediate the of operation of my improved cutter. grooves H and the burr removing portion I. 'I'he Figure 5 is a plan view of the machine. blank is mounted in a suitable work holder M As illustrated in Figure 3, a twist drill is prowhich has imparted thereto by mechanism (not 40 vided with a plurality of helical grooves A with shown) a simultaneous rotary movement and intermediate segments B which latter are cut axial advancement along the line 1--1 of Figaway in rear of the advance edge C to provide a ure 4. 'The cutter J is mounted to rotate in a clearance indicated at D. In the cutting of the plane at an angle to the axis of the work correhelical grooves A the plane of rotation of the sponding substantially to the helical angle of adcutter is voblique to the axis of the blank to provancement of the blank. Thus when the cutter duce the desired helical angle, and consequently is fed into the blank the portions G and F of the it would be impossible to simultaneously fashion same tooth are never in simultaneous operation the portions A and D by a single cutting edge. but these portions G and F of different teeth are "o For this reason it has been the practice in the operating simultaneously. The portion G is oppast to perform these operations successively with erating on a longitudinally advancing portion of different tools. the blank indicated by the line 4 4 at the same The principle of operation of my improved cuttime the portion F is operating upon another ter is illustrated in the diagram, Figure 4, which portion of the blank along the line 3 3. The 5- represents an oblique cross section through the groove I-I between the portions G and I will leave a portion adjacent to the edge C of the original diameter of the blank while the portion I will remove the burr which would otherwise be formed between the portions D and A.

What I claim as my invention is:

1. A rotary cutter for forming twist drills comprising a circular series of like teeth, each having a projecting groove cutting portion, `a narrow re.- cess adjacent to one side'thereof for clearing the work and a clearance cutting portion extending laterally from said recess. 

